Integrated circuit device with optically coupled layers

ABSTRACT

Optical coupling between a first waveguide in a first layer of an integrated circuit device and a second waveguide in a second layer of the integrated circuit device vertically separated from the first layer is described. An optical signal is propagated through a spheroidal element optically coupled to each of the first and second waveguides and positioned between the first and second layers.

FIELD

This patent specification relates to coupling signals between differentlayers of an integrated circuit device.

BACKGROUND

Integrated circuit devices have become essential components in a widevariety of products ranging from computers and robotic devices tohousehold appliances and automobile control systems. New applicationscontinue to be found as integrated circuit devices become increasinglycapable and fast while continuing to shrink in physical size and powerconsumption. As used herein, integrated circuit device refers broadly toa device having one or more integrated circuit chips performing at leastone electrical and/or optical function, and includes both single-chipand multi-chip devices. In multi-chip devices, each integrated circuitchip is usually separately fabricated or “built up” from a substrate,and the resultant chips are bonded together or otherwise coupled into acommon physical arrangement.

Advances in integrated circuit technology continue toward reducing thesize of electrical circuits to smaller and smaller sizes, such that anentire local electrical circuit (e.g., a group of memory cells, a shiftregister, an adder, etc.) can be reduced to the order of hundreds ofnanometers in linear dimension, and eventually even to tens ofnanometers or less. At these physical scales and in view ofever-increasing clock rates, limitations arise in the data ratesachievable between different parts of the integrated circuit device,with local electrical circuits having difficulty communicating with“distant” electrical circuits over electrical interconnection lines thatmay be only a few hundred or a few thousand microns long.

To address these issues, proposals have been made for opticallyinterconnecting different electrical circuits in an integrated circuitdevice. For example, in the commonly assigned U.S. 2005/0078902A1, aphotonic interconnect system is described that avoids high capacitanceelectric interconnects by using optical signals to communicate databetween devices.

As part of such optical interconnection schemes, optical couplingbetween planar waveguides located on different integrated circuit layersis often needed. In a simplest proposal applicable to inter-chipcoupling, two chips are mounted side-by-side such that an edge facet ofa first waveguide on the first chip directly abuts an edge facet of asecond waveguide on the second chip. In another proposal, an opticalfiber is used to transfer optical signals between the two edge facets ofthe different chips. In yet another proposal, an optical fiber is usedto couple between a surface-emitting source on the first chip and adetector on the second chip, each chip having electrical-to-optical(E-O) and optical-to-electrical (O-E) converter(s) as necessary.However, issues arise for such proposals that limit their operationalscalability (e.g., the number of optical interconnections achievablebetween chips) and/or the amount of achievable device compactness.

Vertical optical coupling schemes have also been proposed in which anoptical signal is transferred between planar waveguides located onfacing layers of vertically arranged chips, the vertical arrangementproviding for a smaller footprint while also accommodating a largernumber of optical interconnections between the facing chips. Proposalsinclude the use of angled reflecting structures and/or gratingstructures for urging vertical projection out of one planar waveguideand corresponding vertical collection into the other planar waveguide.

Issues arise, however, in relation to optical coupling efficiency,especially as the vertical spacing between the planar waveguides isincreased. Increases in vertical spacing between the two waveguidinglayers may be desirable in many circumstances, such as for accommodatingdifferent chip assembly methods, enhancing heat dissipation, reducingcrosstalk between facing electrical elements, accommodating verticalsurface features on the facing surfaces, or for a variety of otherreasons. Other issues include one or more of device complexity,alignment issues, fabrication cost, and mechanical stability during orafter device fabrication. Still other issues arise as would be apparentto one skilled in the art upon reading the present disclosure. It wouldbe desired to provide for optical coupling between different layers ofan integrated circuit device, whether such layers be all-optical orelectro-optical, in a manner that addresses one or more of these issues.

SUMMARY

In one embodiment, a method for coupling an optical signal from a firstwaveguide in a first layer of an integrated circuit device to a secondwaveguide in a second layer of the integrated circuit device isprovided, the second layer being vertically separated from the firstlayer. The optical signal is propagated through a spheroidal elementoptically coupled to each of the first and second waveguides andpositioned between the first and second layers.

Also provided is an integrated circuit device comprising a first layerincluding a first waveguide and a second layer including a secondwaveguide, the first and second layers being vertically separated. Aspheroidal element is optically coupled to each of the first and secondwaveguides and positioned between the first and second layers. Thespheroidal element facilitates coupling of an optical signal between thefirst waveguide and the second waveguide.

Also provided is an apparatus comprising a vertical arrangement ofintegrated circuit layers including a first layer and a second layer. Afirst waveguide is formed in the first layer and a second waveguide isformed in the second layer. Spheroidal coupling means in opticalcommunication with each of the first and second waveguides is providedfor coupling an optical signal therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of an integrated circuit deviceaccording to an embodiment;

FIG. 2 illustrates a side cut-away view of an integrated circuit deviceaccording to an embodiment;

FIGS. 3A-3C illustrate optical spectra associated with the integratedcircuit device of FIG. 2;

FIG. 4 illustrates a perspective view of a lower layer and a pluralityof spheroidal elements of an integrated circuit device according to anembodiment;

FIG. 5 illustrates a side cut-away view of an integrated circuit deviceaccording to an embodiment;

FIG. 6 illustrates a side cut-away view of an integrated circuit deviceaccording to an embodiment; and

FIG. 7 illustrates a side cut-away view of an integrated circuit deviceaccording to an embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a perspective view of an integrated circuit device102 according to an embodiment, comprising a lower layer 104 containinga first waveguide 106 and an upper layer 108 containing a secondwaveguide 110. The layers 104 and 108 may be from two differentintegrated circuit chips that have been glued together, bonded together,or otherwise assembled into a vertical arrangement. Alternatively, thelayers 104 and 108 may in a common integrated circuit chip. As usedherein, a layer of an integrated circuit device refers to a verticallycontiguous slab-like subvolume of the integrated circuit device. It isto be appreciated that a layer may itself comprise a plurality ofmaterial sub-layers having relatively complex structures andfunctionalities. Thus, for example, the layers 104 and 108 may eachcomprise several adjacent sub-layers of differing materials formed,processed, patterned, or otherwise fabricated to achieve variouselectrical, electrooptical, and/or optical functionalities.

The layers 104 and 108 may both be all-optical or may both beelectrooptical. Alternatively, one of the layers 104 and 108 may beall-optical and the other may be electro-optical. In one embodiment, thelower layer 104 may comprise densely-packed arrays of electricalcircuits, each being laterally adjacent to a nearby opticalcommunications port having O-E and E-O conversion elements, while theupper layer 108 may comprise an “optical LAN” facilitating informationtransfer of information among “distant” electrical circuits on the layer104. In another embodiment, the layers 104 and 108 may be used forfacilitating the photonic interconnect system described in the commonlyassigned U.S. 2005/0078902A1, supra.

According to an embodiment, integrated circuit device 102 furthercomprises a spheroidal element 114 positioned between the lower layer104 and the upper layer 108, the spheroidal element 114 being opticallycoupled to each of the first waveguide 106 and the second waveguide 110such that an input optical signal 112 propagating along the firstwaveguide 106 is coupled into an output optical signal 116 in the secondwaveguide 110. In one embodiment, the spheroidal element 114 isconfigured and dimensioned to sustain a whispering gallery mode (WGM)resonance at a frequency of the optical signal 112, with WGM resonancemodes being indicated by arrows along a propagation loop 118 in FIG. 1.When configured to achieve a WGM resonance condition at one or morefrequencies, the spheroidal element 114 propagates light analogously todevices variously referenced in the literature as sphericalmicroresonators, whispering gallery mode microresonators, sphericalcavities, whispering gallery mode cavities, spherical dielectriccavities, and resonant spherical cavities.

The spheroidal element 114 comprises a material having a higher index ofrefraction than that of the surrounding material, which can be air or alow-index material. Light propagates in a curved path along an outerperiphery of the spheroidal element 114 by total internal reflection,the spheroidal element 114 having a diameter that is generally largerelative to the wavelength of the light. Generally speaking, a WGMresonance condition can arise where the circumferential path lengthcorresponds to an integer number of wavelengths of the light. In anembodiment where the spheroidal element 114 is a solid microsphere withdiameter D surrounded by air and having a refractive index of n_(s), theWGM resonance condition can be characterized by Eq. (1) below:$\begin{matrix}{\frac{M\quad\lambda}{n_{s}f} = D} & \left\{ 1 \right\}\end{matrix}$

In the above equation, λ is the free space wavelength of the light, M isan integer substantially greater than 1 (M>>1) and in practice oftensubstantially greater than 100 (M>>100), and f is a parameter-dependentfactor that is less than 1 but that approaches 1 as M growssubstantially larger than 100. Generally speaking, the parameter f willbe dependent on other parameters such as particular geometries andpolarizations used, as well as the particular resonance mode excited.Microspheres fabricated using known methods, such as silica microspheresshaped by surface tension forces, have been demonstrated to sustain WGMresonances with very high quality factors Q (a measure relating to aratio of stored modal energy versus cavity losses), for example, 10000and greater. In general, the light is laterally confined to within a fewwavelengths on either side of an x-z plane passing through a center ofthe spheroidal element 114. The WGM resonance condition of Eq. (1) isachieved at a periodic succession of peak wavelengths, eachcorresponding to a successive value of the integer M, the peakwavelengths being approximately separated by a distance Δλ set forth inEq. (2): $\begin{matrix}{{\Delta\quad\lambda} \approx \frac{\lambda^{2}}{n_{s}S}} & \left\{ 2 \right\}\end{matrix}$

It is to be appreciated that the use of a microsphere for the spheroidalelement 114, which is presented for clarity of description above, is butone of many different types of spheroidal elements that can be used inaccordance with the present teachings. More generally, the spheroidalelement 114 can have a variety of different shapes, materialcompositions, structural compositions, and sizes without departing fromthe scope of the present teachings. As used herein, the term spheroidalvolume broadly includes any solid volume providing an at least roughlycircular or ellipsoidal propagation loop within a plane passingtherethrough, while also having at least some degree of laterallyarcuate shape along a periphery of the propagation loop to maintain thelight near that plane. Thus, for example, the spheroidal element 114 ofFIG. 1 confines the optical signal to the propagation loop 118 within acentral x-z plane passing therethrough, and also provides a laterallyarcuate shape in the y-direction along a periphery of the propagationloop to maintain light near that central x-z plane. A wide variety ofdifferent shapes can be used as the spheroidal element 114 including,but not limited to: ellipsoidal shapes having relatively low aspectratios, ellipsoidal shapes having relatively high aspect ratios; andshapes that approximate such ellipsoidal shapes near a central planepassing therethrough but that otherwise deviate from such shape awayfrom that central plane (e.g., football, egg, or cigar-shaped elements,truncated ellipsoids that are “chopped off” at outlying ends, etc.).However, for clarity of description, and not by way of limitation, thespheroidal element 114 is characterized hereinbelow as having a singlesize dimension D corresponding to a diameter of a spherical element. Oneskilled in the art would be readily able to derive, eithermathematically or empirically, appropriate corresponding dimensions fornon-spherical cases and/or non-circular peripheral propagation paths.

A wide variety of different material and structural compositions can beused for the spheroidal element 114, including solid structures,hollowed structures, and coated structures. For example, the spheroidalelement can comprise a low-index core region surrounded by a coating ofhigh-index material. Generally speaking, modal stability and deviceperformance is enhanced where the spheroidal element 114 has asubstantially higher refractive index (e.g., 2:1 or 3:1) than thesurrounding material at its outer surface. Generally speaking, the sizeof the spheroidal element 114 can be made smaller as this refractiveindex ratio is increased. One particularly suitable material for thespheroidal element 114 is chalcogenide glass, which has a refractiveindex in the range of 2.4-2.8. Other suitable materials include otherhigh-index glasses and sapphire. If a high-index outer coating is used,that coating should have a thickness of at least about λ/2n_(c) forsufficient propagation of an optical signal around the periphery of thespheroidal element 114, where n_(c) is the refractive index of thecoating.

The waveguides 106 and 110 can be formed onto or into the layers 104 and108 according to any of a variety of different waveguiding materialsystems. In one embodiment, silicon-on-insulator (SOI) substrates and anSi/SiO₂ material system is used. In another embodiment, an SiN/SiO₂material system is used. Other suitable material systems include, butare not limited to, GaAs/AlGaAs, InGaAsP/InP, and other III-V materialsystems.

A wide variety of different sizes for the spheroidal element 114 and awide variety of different wavelengths for the optical signal 112 arewithin the scope of the present teachings. By way of example and not byway of limitation, the optical signal 112 may be in the range of400-1600 nm and the spheroidal element 114 may be between 20 μm and 2 mmin size.

In one embodiment, the spheroidal element 114 is dimensioned andconfigured relative to the waveguides 106 and 110 such that evanescentcoupling is achieved for the propagating optical signal, wherein anevanescent field of the WGM modes overlaps with evanescent fields of thewaveguides 106 and 110 in a phase-matched manner. Generally speaking,very high coupling efficiencies between the input optical signal 112 andthe output optical signal 116, such as 90 percent or greater, can beachieved when such evanescent coupling is used. In other embodiments,one or both of the waveguides 106/110 can be coupled into the spheroidalelement 114 using a non-evanescent coupling method, such as directcoupling by facet contact.

In some embodiments, the waveguides 106 and 110 are identical to eachother in the vicinity of the spheroidal element 114, and the spheroidalelement 114 is configured and positioned in a symmetric manner relativeto each of them, such that a two-way vertical coupler is achieved. Inother embodiments, these structures and/or couplings are made asymmetricin a manner that optimizes coupling in one direction, usually at theexpense of coupling in the other direction.

Particular parameters for achieving coupling between the input opticalsignal 112 and the output optical signal 116 will be highly dependent onthe particular wavelengths, refractive indices, loss coefficients,polarizations, coupling geometries, and physical dimensions used, aswell as the particular resonance modes that are to be excited. By way ofexample only, and not by way of limitation, for a typical opticalcommunications wavelength of 1.55 μm, Si/SiO₂ waveguides can be usedwith a chalcogenide glass spheroidal element 160 μm in diameter. In viewof the present disclosure, one skilled in the art would be readily ableto mathematically and/or empirically determine suitable combinations ofsuch parameters providing sufficient optical coupling.

FIG. 2 illustrates a side cut-away view of an integrated circuit device202 according to an embodiment, comprising a lower layer 204 containinga first waveguide 206, an upper layer 208 containing a second waveguide210, and a spheroidal element 214 evanescently coupled to each of thewaveguides 206 and 210 at evanescent coupling regions 222 and 224,respectively, such that an input optical signal 212 in the firstwaveguide 206 couples through the spheroidal element 214 into an outputsignal 216 in the second waveguide 210. In this example and hereinbelow,the waveguiding structures and their associated layers comprise Si/SiO₂material systems by way of non-limiting example.

In the embodiment of FIG. 2, an intermediate layer 220 having a verticaldimension coextensive with that of the spheroidal element 214 is filledat locations therearound with a low-index material such polyamide,polymethyl-methacrylate (PMMA) or other various low-index liquids, gels,pastes, or solid materials. In other embodiments, the intermediate layer220 can simply comprise air at those locations.

Also shown in FIG. 2 are spacing layers 207 and 211, which may compriseSiO₂, serving as both waveguide cladding and as spacers for optimizingthe evanescent couplings by virtue of careful selection of theirrespective thicknesses T1 and T2. By way of nonlimiting example, thethicknesses T1 and T2 may be on the order of 100 nm. In otherembodiments, the thicknesses T1 and/or T2 may be zero (i.e., the layers207/211 are omitted).

Also shown in FIG. 2 is an optical signal 226 representing a portion ofthe optical signal 212 that does not couple into the spheroidal element214. For purposes of clarity of description hereinbelow, it is assumedthat cavity losses are negligible and that the “drop” coupling at region222 from the first waveguide 206 into the spheroidal element 214 isidentical to the “add” coupling at region 224 from the spheroidalelement 214 into the second waveguide 210. Accordingly, for anyparticular wavelength λ, if there is a ratio of signal powersP₂₂₆/P₂₁₂(λ) near zero, then there is a very high vertical couplingefficiency between the lower and upper waveguides 206 and 210 for thatwavelength, while a very low vertical coupling efficiency for thatwavelength is indicated if the ratio P₂₂₆/P₂₁₂(λ) is near 1.0.

FIGS. 3A-3C illustrates optical spectra associated with the integratedcircuit device 202 of FIG. 2. FIG. 3A illustrates a curve 302 ofP₂₂₆/P₂₁₂(λ), with dips corresponding to WGM resonant modes separated bya uniform spacing Δλ according to Eq. (2), supra, the dips beingassociated with wavelengths of high vertical coupling efficiency. In oneembodiment, the optical signal 212 is a wavelength-division multiplexed(WDM) signal having adjacent center wavelengths at λ1, λ2, λ3, etc. Inone embodiment (see FIG. 3B, spectra 302 and 304), successive centerwavelengths of the WDM signal are designed to correspond to successiveWGM resonance modes of the spheroidal element 214. In another embodiment(see FIG. 3C, spectra 302′ and 306), successive center wavelengths ofthe WDM signal are designed to correspond to a single WGM resonance modeof the spheroidal element 214. More generally, the spheroidal element214 will sustain high WGM resonance (and therefore high verticalcoupling efficiency) for a first subset of component wavelength rangesof the optical signal 212, and will have diminished WGM resonance (andtherefore low vertical coupling efficiency) for a second subset ofcomponent wavelength ranges. Various optical filtering schemes andmultiplexing/demultiplexing schemes can therefore be used in conjunctionwith the vertical coupling provided by the spheroidal element 214.

The shape of the curve 302 for P₂₂₆/P₂₁₂(A) is characterized in part bya WGM resonance bandwidth W, expressed as a percentage of the WGM modeseparation Δλ, and by a peak height percentage H. The values for W, H,and Δλ can be highly influenced by variation of different materialparameters, geometries, and materials used in the vertical couplingscheme of FIG. 2. By way of example, reducing the Q of the spheroidalelement 214 by using lossier materials serves to increase the bandwidthW (although decreasing the peak height percentage H). By way of exampleand not by way of limitation, for the 160 μm chalcogenide spheroidalelement mentioned previously, a Q of 10000 or less is required toaccommodate 10 Gbps modulation of any particular WDM channel near 1.55μm. Increasing the refractive index ns or diameter of the spheroidalelement reduces the WGM mode separation Δλ. Increasing the thickness T1of the spacer layer 207 generally reduces W but can positively ornegatively influence H depending on the present thickness T1 and otherdetails.

FIG. 4 illustrates a perspective view of a lower layer 404 of anintegrated circuit device 402 according to an embodiment. An upper layerof the integrated circuit device 402 is omitted from FIG. 4 for clarityof presentation, with only waveguides 410 a-410 b therein being shown asdotted lines. According to an embodiment, the integrated circuit device402 comprises at least three spheroidal elements 414 a-414 c ofgenerally similar dimension positioned in a non-collinear manner betweenthe lower layer 404 and the upper layer. Mechanical stability isfacilitated, either during the fabrication process, such as during thecuring of a paste into a solid material, or on a long term basis, suchas when only air is present.

As indicated in FIG. 4, spheroidal element 414 a provides for verticalcoupling of an input optical signal 412 a in a first waveguide 406 a ofthe lower layer 404 into an output optical signal 416 a in a secondwaveguide 410 a of the upper layer, while spheroidal element 414 bprovides for vertical coupling of an input optical signal 412 b in athird waveguide 410 b of the upper layer into an output optical signal416 b in a fourth waveguide 406 b of the lower layer 404. In contrast,spheroidal element 414 c is “dark” and provided only for mechanicalstability.

Also shown in FIG. 4 are alignment structure groups 430 a-430 ccorresponding respectively to the spheroidal elements 414 a-414 c, forfacilitating their alignment and placement during the fabrication of theintegrated circuit device and for further facilitating mechanicalstability afterward. Difficulties in alignment and placement of thespheroidal elements 414 a-414 c, which are usually separatelypre-fabricated, are thereby at least partially alleviated. The alignmentstructure groups 430 a-430 c form part of the lower layer 404 and maycomprise the same material as, or a different material than, thesurrounding surface of the lower layer 404. Each of the alignmentstructure groups 430 a-430 c comprises at least three alignmentstructures or “bumps” for contacting the corresponding spheroidalelement at locations not intersecting a propagation path of the opticalsignal, so as not to interfere with the vertical coupling.

FIG. 5 illustrates a side cut-away view of an integrated circuit deviceaccording to an embodiment comprising a lower layer 502 containing afirst waveguide 504, an upper layer 506 containing a second waveguide508, and a spheroidal element 510 providing for vertical coupling of aninput optical signal “IN” in the first waveguide 504 into an outputsignal “OUT” in the second waveguide 508. According to the embodiment ofFIG. 5, the spheroidal element 510 is directly coupled with thewaveguides 504 and 508 by contact with respective facets 505 and 507thereof. The optical signal propagates in a non-resonant manner directlybetween the facets 505 and 507, in a single trip along an outer arc ofthe spheroidal element 510 as shown by arrows 512.

FIG. 6 illustrates a side cut-away view of an integrated circuit deviceaccording to an embodiment particularly advantageous from a fabricationperspective when it is desired to built up the lower and upper layersfrom a common substrate. A lower layer 602 having a first waveguide 604is formed, and an intermediate layer 606 is formed thereabove bydepositing a uniform-thickness layer of a first low-index material 608.A trench 610 is created in the intermediate layer 606, a spheroidalelement 612 is deposited in the trench. The trench 610 is then flowablybackfilled with a second low-index material 614, which may be an uncuredphase of the same compound as material 608 or which may be a differentcompound. An upper layer 616 having a second waveguide 618 is thenformed thereabove. Thus, the first and second layers 602 and 616 areseparated by the low-index intermediate layer 606, and the spheroidalelement 612 is located within the trench 610 formed in the intermediatelayer 606.

FIG. 7 illustrates a side cut-away view of an integrated circuit deviceaccording to an embodiment comprising a vertical assembly of layersincluding a first layer 702 containing a first waveguide 710 on an uppersurface thereof and a second layer 704 containing a second waveguide 712on a lower surface thereof. A first spheroidal element 708 provides forvertical coupling of an input optical signal I1 in the first waveguide710 into an output signal O1 in the second waveguide 712. The secondlayer 704 further contains a third waveguide 714 on an upper surfacethereof. The vertical assembly further comprises a third layer 706containing a fourth waveguide 718 on a lower surface thereof. A secondspheroidal element 716 provides for vertical coupling of an inputoptical signal I2 in the third waveguide 714 into an output signal O₂ inthe fourth waveguide 718.

Fabrication of integrated circuit devices according to one or more ofthe embodiments can be achieved using known integrated circuitfabrication methods including, but not limited to: deposition methodssuch as chemical vapor deposition (CVD), metal-organic CVD (MOCVD),plasma enhanced CVD (PECVD), chemical solution deposition (CSD), sol-gelbased CSD, metal-organic decomposition (MOD), Langmuir-Blodgett (LB)techniques, thermal evaporation/molecular beam epitaxy (MBE), sputtering(DC, magnetron, RF), and pulsed laser deposition (PLD); lithographicmethods such as optical lithography, extreme ultraviolet (EUV)lithography, x-ray lithography, electron beam lithography, focused ionbeam (FIB) lithography, and nanoimprint lithography; removal methodssuch as wet etching (isotropic, anisotropic), dry etching, reactive ionetching (RIE), ion beam etching (IBE), reactive IBE (RIBE),chemical-assisted IBE (CAIBE), and chemical-mechanical polishing (CMP);modifying methods such as radiative treatment, thermal annealing, ionbeam treatment, and mechanical modification; and assembly methods suchas wafer bonding, surface mount, and other wiring and bonding methods.

Whereas many alterations and modifications of the embodiments will nodoubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that theparticular embodiments shown and described by way of illustration are inno way intended to be considered limiting. By way of example, while inone or more the above embodiments the spheroidal element and theinput/output waveguides are passive components, in other embodimentsactive components may be used that, responsive to one or more electricaland/or optical control signals, serve to modulate, amplify, filter,multiplex/demultiplex, or otherwise control a property of the opticalsignal.

By way of further example, although evanescent coupling and directcoupling by facet contact are described for coupling the planarwaveguides with the spheroidal element, in other embodiments the opticalsignal may couple into the spheroidal element by angular projection fromgrating structures, reflecting structures, or various modulated opticalsources. By way of still further example, although the present teachingsare particularly advantageous in the context of ever-shrinking hybridoptoelectronic devices, they are readily applicable to all-opticalintegrated circuit devices (e.g., as used in all-optical computingdevices), as well as to larger-sized devices.

By way of even further example, although one or more of the embodimentsis particularly useful for obviating the need for optical fiberconnections between chips, optical fibers may still be used for variousother purposes in the integrated circuit device (e.g., importinghigher-power optical carrier signals from off-chip lasers) withoutdeparting from the scope of the present teachings. By way of stillfurther example, although one or more of the embodiments is particularlyuseful where the layers are each contained on integrated circuit chips,the scope of the present teachings includes scenarios where one layer ison an integrated circuit chip, and the other layer is on aprinted-circuit board or other type of back-plane/packaging assembly.Thus, reference to the details of the described embodiments are notintended to limit their scope.

1. A method for coupling an optical signal from a first waveguide in afirst layer of an integrated circuit device to a second waveguide in asecond layer of the integrated circuit device vertically separated fromthe first layer, comprising propagating the optical signal through afirst spheroidal element optically coupled to each of the first andsecond waveguides and positioned between said first and second layers,said integrated circuit device comprising a vertical assembly of aplurality of integrated circuit chips, said first layer being an upperlayer of a first of said integrated circuit chips and said second layerbeing a lower layer of a second of said integrated circuit chips, saidspheroidal element facilitating optical communications between saidfirst and second integrated circuit chips, said integrated circuitdevice further comprising at least two additional spheroidal elements ofsimilar dimensions as said first spheroidal element, said additionalspheroidal elements being positioned between said first and secondlayers and laterally distributed relative to said first spheroidalelement such that mechanical stability of said vertical assembly isfacilitated.
 2. The method of claim 1, wherein said first spheroidalelement sustains a whispering gallery mode (WGM) resonance at afrequency of the optical signal.
 3. The method of claim 2, wherein thefirst spheroidal element is evanescently coupled with each of said firstand second waveguides at said frequency of said optical signal.
 4. Themethod of claim 2, wherein said first spheroidal element is directlycoupled with the first waveguide by contact with a facet thereof.
 5. Themethod of claim 1, wherein said first spheroidal element is directlycoupled with each of the first and second waveguides by contact withrespective facets thereof, and wherein the optical signal propagates ina non-resonant manner directly between said facets along an outer arc ofthe first spheroidal element.
 6. (canceled)
 7. (canceled)
 8. The methodof claim 1, said first and second layers being separated by a gap, saidgap having a thickness associated with a dimension of said firstspheroidal element, wherein said gap is occupied by one of air and alow-index material at locations laterally surrounding said firstspheroidal element.
 9. The method of claim 1, said second integratedcircuit chip having an upper layer including a third waveguide therein,said integrated circuit device further comprising a third integratedcircuit chip having a lower layer including a fourth waveguide therein,said integrated circuit device further comprising a further additionalspheroidal element positioned between said upper layer of said secondintegrated circuit chip and said lower layer of said third integratedcircuit chip and optically coupled to each of said third and fourthwaveguides for facilitating optical communications between said secondand third integrated circuit chips.
 10. The method of claim 1, whereinsaid first layer comprises at least three alignment structurescontacting said first spheroidal element at locations not intersecting apropagation path of the optical signal therethrough, said alignmentstructures facilitating positional stability of the first spheroidalelement on said first layer during formation of said vertical assembly.11. The method of claim 1, wherein said first layer is a lower layer ofan integrated circuit chip, and wherein said second layer is an upperlayer of a printed-circuit board.
 12. The method of claim 1, saidoptical signal being a wavelength division multiplexed (WDM) signalcomprising a plurality of component frequency ranges, said firstspheroidal element sustaining a whispering gallery mode (WGM) resonancefor a subset of said component frequency ranges, whereby said firstspheroidal element transfers the optical signal from said firstwaveguide into said second waveguide for said subset of componentfrequency ranges and does not transfer the optical signal from saidfirst waveguide into said second waveguide for the other componentfrequency ranges.
 13. The method of claim 1, said optical signal being afirst optical signal, a one of said at least two additional spheroidalelements being optically coupled between a third waveguide in saidsecond layer and a fourth waveguide in said first layer, furthercomprising coupling a second optical signal from said third waveguide insaid second layer to said fourth waveguide in said first layer bypropagating the second optical signal through said one of said at leasttwo additional spheroidal elements.
 14. (canceled)
 15. (canceled) 16.The method of claim 1, wherein at least one of said first waveguide,said second waveguide, and said first spheroidal element comprises anactive material controlled by at least one of an electrical controlsignal and an optical control signal, and wherein said coupling theoptical signal includes at least one of modulating, amplifying,multiplexing, and demultiplexing the optical signal.
 17. An integratedcircuit device, comprising: a first layer including a first waveguide; asecond layer including a second waveguide, the first and second layersbeing vertically separated; and a first spheroidal element opticallycoupled to each of the first and second waveguides and positionedbetween said first and second layers, the first spheroidal elementfacilitating coupling of an optical signal between said first waveguideand said second waveguide, said integrated circuit device comprising avertical assembly of a plurality of integrated circuit chips, said firstlayer being an upper layer of a first of said integrated circuit chipsand said second layer being a lower layer of a second of said integratedcircuit chips, said integrated circuit device further comprising atleast two additional spheroidal elements of similar dimensions as saidfirst spheroidal element, said additional spheroidal elements beingpositioned between said first and second layers and laterallydistributed relative to said first spheroidal element such thatmechanical stability of said vertical assembly is facilitated.
 18. Theintegrated circuit device of claim 17, wherein the optical signal has awavelength between about 400-1600 nm, and wherein said first spheroidalelement has an average major diameter between about 20 μm-2 mm.
 19. Theintegrated circuit device of claim 18, wherein said first spheroidalelement comprises chalcogenide glass, and wherein said first and secondwaveguides each comprise one of an Si/SiO₂ waveguide structure and aIII-V waveguide structure.
 20. The integrated circuit device of claim17, wherein said first spheroidal element comprises one of a sphericalelement, an ellipsoidal element, a laterally truncated sphericalelement, and a laterally truncated ellipsoidal element.
 21. Theintegrated circuit device of claim 17, wherein the first spheroidalelement is evanescently coupled with each of said first and secondwaveguides at a wavelength of the optical signal and is configured tohave a whispering gallery mode (WGM) resonance at said wavelength. 22.The integrated circuit device of claim 17, wherein said first spheroidalelement is directly coupled with the first waveguide by contact with afacet thereof.
 23. The integrated circuit device of claim 17, whereinsaid first spheroidal element is directly coupled with each of the firstand second waveguides by contact with respective facets thereof, andwherein the optical signal propagates in a non-resonant manner directlybetween said facets along an outer arc of the first spheroidal element.24. The integrated circuit device of claim 17, said second integratedcircuit chip having an upper layer including a third waveguide therein,said integrated circuit device further comprising: a third integratedcircuit chip having a lower layer including a fourth waveguide therein;and a further additional spheroidal element positioned between saidupper layer of said second integrated circuit chip and said lower layerof said third integrated circuit chip and optically coupled to each ofsaid third and fourth waveguides for facilitating optical communicationsbetween said second and third integrated circuit chips.
 25. (canceled)26. The integrated circuit device of claim 17, said first layer furthercomprising at least three alignment structures contacting said firstspheroidal element at locations not intersecting a propagation path ofthe optical signal therethrough, said alignment structures facilitatingpositional stability of the first spheroidal element on said firstlayer.
 27. The integrated circuit device of claim 17, wherein said firstlayer is a lower layer of an integrated circuit chip, and wherein saidsecond layer is an upper layer of a printed-circuit board.
 28. Theintegrated circuit device of claim 17, said optical signal being awavelength division multiplexed (WDM) signal comprising a plurality ofcomponent frequency ranges, said first spheroidal element sustaining awhispering gallery mode (WGM) resonance for a subset of said componentfrequency ranges, whereby said first spheroidal element transfers theoptical signal from said first waveguide to said second waveguide forsaid subset of component frequency ranges and does not transfer theoptical signal from said first waveguide to said second waveguide forthe other component frequency ranges.
 29. (canceled)
 30. The integratedcircuit device of claim 17, wherein at least one of said firstwaveguide, said second waveguide, and said first spheroidal elementcomprises an active material controlled by at least one of an electricalcontrol signal and an optical control signal, and wherein said couplingof the optical signal includes at least one of modulating, amplifying,multiplexing, and demultiplexing the optical signal.
 31. An apparatus,comprising: a vertical arrangement of integrated circuit layersincluding a first layer and a second layer; a first waveguide formed insaid first layer and a second waveguide formed in said second layer; andspheroidal coupling means in optical communication with each of saidfirst and second waveguides for coupling an optical signal therebetween,wherein said spheroidal coupling means comprises a first spheroidalelement lying between said first and second layers, and wherein saidapparatus further comprises at least two additional spheroidal elementsof similar dimensions as said first spheroidal element also positionedbetween said first and second layers and laterally distributed relativeto said first spheroidal element such that mechanical stability of saidvertical arrangement is facilitated.
 32. The apparatus of claim 31,wherein said first spheroidal element comprises a sphericalmicroresonator.
 33. The apparatus of claim 31, wherein said firstspheroidal element is selected from the group consisting of: a sphericalmicroresonator, an ellipsoidal microresonator, a laterally truncatedspherical microresonator, and a laterally truncated ellipsoidalmicroresonator.
 34. The apparatus of claim 31, wherein said spheroidalcoupling means is evanescently coupled with each of said first andsecond waveguides at a wavelength of the optical signal and isconfigured to have a whispering gallery mode (WGM) resonance at saidwavelength.
 35. The apparatus of claim 31, wherein said spheroidalcoupling means is directly coupled with each of the first and secondwaveguides by contact with respective facets thereof, and wherein theoptical signal propagates in a non-resonant manner directly between saidfacets along an outer arc of the spheroidal coupling means. 36.(canceled)
 37. The apparatus of claim 31, said spheroidal coupling meansbeing a first spheroidal coupling means and said optical signal being afirst optical signal, said apparatus further comprising: a third layerpositioned above said second layer and containing a third waveguide; anda second spheroidal coupling means optically coupling a second opticalsignal between said third waveguide and a fourth waveguide contained onsaid second layer, wherein said second spheroidal coupling meanscomprises a further additional spheroidal element lying between saidsecond and third layers.
 38. The apparatus of claim 31, wherein at leastone of said first waveguide, said second waveguide, and said spheroidalcoupling means comprises an active material controlled by at least oneof an electrical control signal and an optical control signal, andwherein said coupling the optical signal includes at least one ofmodulating, amplifying, multiplexing, and demultiplexing the opticalsignal.